The overall purpose of this research is to develop a functional model for the brain stem integration of afferent stimuli arising from peripheral and central chemoreceptor areas. Work completed to date has focused upon the respiratory areas of lower midbrain, pons and upper medulla. It has been demonstrated that among respiratory units rostral to midpons, the pneumotaxic center uniquely influences the operational "set point" for respiratory activity. Moreover, subsequent to pneumotaxic center ablation, hypercapnia-induced minute volumes are significantly suppressed whereas the comparable minute volume responses to hypoxia may be maintained. This former result implies that this is a differential integration by the brain stem of peripheral and central chemoreceptor afferent influences. More recent experiments have focused upon the anatomical identification of sites within the brain stem having a role in the generation of respiratory tidal volume. Results obtained have demonstrated that the reticular formation of lower pons and upper medulla serve primary functions in tidal volume generation for both hypercapnic and hypoxic stimuli. Efferent activity from these tidal volume generating sites of pons and medulla has been shown to converge upon midline structures of the medulla.